WO2001060724A1

WO2001060724A1 - Pneumatic conveyor equipped with bottom guide

Info

Publication number: WO2001060724A1
Application number: PCT/FR2000/000405
Authority: WO
Inventors: Joël TRENEL; Carlos Rodrigues
Original assignee: Netra Systems
Priority date: 2000-02-17
Filing date: 2000-02-17
Publication date: 2001-08-23
Also published as: US6368027B1; ATE305428T1; EP1255687B1; ES2250102T3; DE60022910D1; AU2000228103A1; EP1255687A1; DE60022910T2

Abstract

The invention concerns a pneumatic conveyor for transporting suspended articles, for example empty plastic bottles B, under the action of air jets. It comprises a longitudinal bottom guide (6) extending along the path of the articles, which comprises two opposite longitudinal guiding walls (7b), and which is positioned or adapted relative to a levitation point for the articles such that an article suspended on the conveyor comes in contact through its base with the inner surface of the two guiding walls by being maintained inclined relative to the vertical and rearwards relative to the transport direction at a minimum conveying angle.

Description

AIR CONVEYOR HAVING A LOWER GUIDE

The present invention relates to the field of pneumatic transport of hanging articles, and more particularly of light articles such as for example empty plastic bottles or flasks, preforms etc.

To transport light articles, and more particularly plastic bottles or the like, it is currently known to use air conveyors equipped with blowing means making it possible to create a plurality of air jets oriented on the articles in their direction. transport.

For articles which can be hung, such as for example plastic bottles having at their neck a collar, use is more particularly of air conveyors which are equipped with a guide rail, more commonly called under-neck guide , along which the articles are guided and transported while being suspended by means of their flange or the like. This type of conveyor is described for example in patent US-A-4,284,370 or also in patent US-A-5,161, 919. It implements a main air duct, commonly called a plenum and extending along the path of the articles, and a blowing channel communicating with the main air sheath via blowing slots or the like. The main duct is supplied with air, for example by means of several fans judiciously distributed over its entire length; this air is exhausted through the blowing slots in the form of a plurality of air jets for propelling the articles along the blowing channel. In US-A-4,284,370, the blowing channel has a rectangular section and the blowing slots are arranged above the guide rail, which makes it possible to propel the articles by blowing above their flange. In patent US-A-5,161,919, the blowing channel has the shape of an inverted V, and the blowing slots are arranged below the guide rail, which makes it possible to propel the articles by blowing under their collar. During their transport, the suspended articles, for example by means of their flange, can tilt laterally with respect to the longitudinal conveying direction, in particular in the curved parts (bends) of the conveyor. To limit this lateral displacement of the articles, it is common practice to date to equip air conveyors with lateral guides disposed on either side of the path of the articles, the spacing between the side guides conditioning ^the angle maximum lateral travel of the articles. Also during their transport, the bottles tend to oscillate longitudinally with respect to the vertical in an alternating forward / backward movement, which affects the quality of conveying, and which moreover causes risks of blocking of the articles, such as by example a front or rear blocking. To compensate for the front / rear oscillations of the articles, it has already been proposed to date in patent US-A-5,421,678 to equip an air conveyor with at least one longitudinal brush which extends along the path of the articles , and which makes it possible to continuously apply to the articles during transport a braking force such that the articles are transported stably by being inclined with respect to the vertical and rearward with respect to the direction of transport of a given angle, hereinafter called the conveying angle. More particularly, in the alternative embodiment illustrated in FIG. 4 of this publication, the conveyor is equipped with two lower and upper pairs of lateral guides referenced 42 and 44 to limit the lateral movement of the articles, and is equipped with a brush referenced 60 and fixed to one of the two lower lateral guides 44. A first drawback of this solution is that the conveying angle depends in particular on the conveying speed and the material of the bottles; furthermore, it is not possible to guarantee a minimum conveying angle. A second drawback is that wear is observed over time with the brush bristles and above all a preferential orientation of the bristles caused by repeated contact with the articles, which results in a change in angle over time. conveying items. It is therefore necessary to maintain the correct conveying angle to regularly adjust the distance between the bristles of the brushes and the body of the articles, and in the long run to replace the used brushes.

The main object of the present invention is to propose a new solution which also makes it possible to improve the conveyability of the suspended articles transported in an air conveyor, by overcoming the problems of front / rear oscillation and lateral movement of the articles. suspended during transport, but which does not have the aforementioned drawbacks of the solution adopted in patent US-A-5,421,678.

This object is achieved by the invention which relates to an air conveyor for the transport of articles suspended under the action of air jets, which conveyor is essentially characterized according to the invention by the implementation of '' a lower longitudinal guide which extends along the path of the articles, which comprises two opposite longitudinal guide walls, and which is positioned or is capable of being positioned relative to the point of levitation of the articles so that '' an article suspended on the conveyor comes into contact at its base with the internal face of the two guide walls while being kept inclined with respect to the vertical and rearward with respect to the direction of transport at a minimum conveying angle (AT). According to the invention, the lower longitudinal guide fulfills the dual function of limiting the lateral movement of the articles and of imposing a minimum conveying angle, which makes it possible to prevent the front / rear oscillation of the articles during transport.

In a preferred embodiment, the conveyor is equipped with means for adjusting the distance separating the lower longitudinal guide and the point of lift of the articles in a vertical direction. A modular air conveyor is thus produced which can quickly and easily be adapted to the format (shape and dimensions) of the items transported. In a particular variant embodiment, the means for forming the transport air jets for propelling the articles along the conveyor are designed so as to generate at least lower air jets which are directed onto the articles below their point of sustenance. Prior to the invention, the implementation of lower transport air jets, which applied to a portion of the articles located below their point of lift, was a source of significant instability of the articles transported, in particular in the case where the articles transported were suspended by means of a load-bearing zone situated clearly above their center of gravity, which is the case for example of the plastic bottles transported while being suspended by means of a protuberance at their neck. To date, we have been forced in this type of conveyor, to limit the risks of instability of the articles, without however eliminating them, to limit the power of the lower transport air jets and / or to position these jets. transport below the closest to the lifting point of the articles, to the detriment of the conveying speed. The implementation of a lower longitudinal guide according to the invention advantageously makes it possible to overcome this drawback, because this guide makes it possible to transport the articles in a tilted back position, and thus to avoid any tilting towards the 'before articles under the action of the lower transport air jets. It thus becomes possible to increase the power of the lower transport air jets and / or to apply these lower transport air jets to any portion of the articles located below their lift point, without harming the conveying stability of articles. Other characteristics and advantages of the invention will appear more clearly on reading the description below of three alternative embodiments of an air conveyor in accordance with the invention, which description is given by way of non-limiting example and with reference to the appended drawings in which: FIG. 1 is a diagrammatic representation in section of a first alternative embodiment of an air conveyor with a multi-position V-shaped lower longitudinal guide,

FIG. 2 is a schematic representation seen from the side of the conveyor of FIG. 1, FIG. 3 is a representation in section of a second alternative embodiment of an air conveyor according to the invention,

- Figure 4 is a schematic sectional representation of a third alternative embodiment of an air conveyor according to the invention.

There is shown in Figure 1 a first alternative embodiment of an air conveyor used for the transport, under the action of air jets, of empty plastic bottles B. Usually, this air conveyor comprises a main blowing duct 1 which is designed to be supplied with pressurized air by means of fans (not shown) regularly distributed along the duct 1. The bottom wall 1 has the blowing duct 1 forms in the central part a recess 2 delimiting a blowing channel 3. In the side walls 2a and 2b of the recess 2 are provided with blowing slots 4, which allow the escape of the pressurized air from the inside of the duct 1 towards the inside of the blowing channel 3 in the form of a plurality air jets directed towards the bottles above their point of lift. The blowing slots 4 will, for example, be regularly distributed over the entire length of the blowing channel 3. For the lifting of the bottles, the air conveyor is equipped with two guides under the neck 5 fixed on the bottom wall 1a of the blowing duct 1 , and which define a support and guide rail for the bottles B along the conveyor.

In the particular example illustrated in Figure 1, there is shown a bottle B suspended on the two guide rails 5 via its flange C. This implementation is not limiting of the invention. In other alternative embodiments, the lift zone of the bottles is not necessarily constituted by their flange but perhaps constituted for example by any protuberance or other equivalent means at the level of any part of their body.

When the blowing duct 1 is supplied with pressurized air, this pressurized air escapes through the slots 4 in the form of a plurality of air jets J (FIG. 2) which are generated above the flange of the bottles B, and which make it possible to propel these bottles along the two guide rails 5 in a given direction of transport shown diagrammatically by the arrow SDT in FIG. 2. According to an essential and new characteristic of the invention, the air conveyor of FIGS. 1 and 2 is equipped with a lower longitudinal guide 6, which extends along the path of the bottles, and which in the example illustrated has substantially in section the shape of a V. In the particular example illustrated, this lower longitudinal guide 6 is formed by a folded sheet 7 having a bottom 7a extending on either side and symmetrically by two inclined longitudinal walls 7b facing each other, hereinafter called guide walls, each of the two walls of guide 7b extending in the upper part by an upper edge 7c. This lower longitudinal guide 6 is mounted on the conveyor below and below the two guide rails 5 so that the axis of symmetry of this guide rail coincides with the axis of SS symmetry of the conveyor, ie essentially the axis of symmetry between the two guide rails 5. This guide rail 6 further extends over all or part of the length of the conveyor.

In the embodiment of FIG. 1, the lower longitudinal guide 6 forms, at the level of the internal face 8 of each longitudinal guide wall 7b_, a plane PP inclined relative to the vertical of an angle E. The two PP planes formed by each guide wall 7b converge towards each other downwards. The guide 6 also forms, at the level of the internal face 8 ′ of each end edge 7 c, a substantially vertical plane P ′ P ′. In an alternative embodiment (not shown), the internal face 8 of each guide wall 7b_ and the internal face 8 'of each edge 7c could be formed directly by the wall of the guide, in which case a guide produced in a material with a low coefficient of friction and, for example, a guide made of stainless steel or a guide made of plastic material such as HDPE (High Density Polyethylene). In the variant illustrated in FIG. 1, the internal faces 8 and 8 ′ of the guide walls 7b_ and of the flanges 7c. are provided with a coating 9 with a very low coefficient of friction. It will for example be a coating made of polytetrafluoroethylene (PTFE). There is shown in Figures 1 and 2, a bottle B, which is suspended on the two guide rails 5 via its flange C. In this position, under the action of its own weight, the bottle comes to contact of the internal face 8 of the two guide walls 7b of the guide 6. More specifically, if one refers to FIG. 2, the distance d, which separates the point of lift of this bottle B (ie guides under neck 5) and guide 6, is adjusted so that when the bottle B is suspended on the guide under neck 5, it comes under the action of its weight in contact with the inner face of the two guide walls 7b_ of guide 6 while being inclined by a minimum conveying angle A.

During transport, under the action of the transport air jets J coming from the blowing slots 4, the bottle is propelled in the direction SDT (FIG. 2). Due to the presence of the two guide walls 7b of the guide 6, this bottle B is transported stably by being inclined towards the rear by a minimum angle A, and any risk of oscillation forwards is avoided. the bottle, which could be detrimental to the conveying stability. The absence of front / rear rocking of the bottles during transport also advantageously makes it possible to avoid the problems of marking the neck of the bottles under their flange in contact with the guides under the neck. Also, by transporting this bottle B at an inclination towards the rear, the contact zones between the collar C and the guides under the neck 5 are limited, which limits friction and improves the conveyability of the bottles. The wear phenomena of the under-neck guides, which are mainly observed with plastic under-neck guides, are further limited. Of course, during transport, the bottle is not necessarily constantly in contact with the two guide walls 7b of the guide 6, its angle of inclination towards the rear relative to the vertical being able to increase, which is the case. for example when a bottle comes into contact and rolls up on a previous bottle, as illustrated in FIG. 2 for the bottle B1 which is in this case tilted backwards with respect to the vertical by an angle winding A 'greater than the conveying angle A.

During normal transport of the bottles B, the two guide walls 7b_ allow both to impose mechanically on the bottles transported B a rearward inclination of a minimum conveying angle A, but also act as lateral guide for the bottles, by preventing the bottles B from tilting from a too large swing angle in a vertical plane and substantially transverse to their direction of transport (that is to say in the plane of FIG. 1). The risk of bottles swaying during transport is greatest in the curved portions of the conveyor (bends). In fact, in these curved portions, the bottles tend, under the effect of centrifugal force, to take off from the internal face of the two guide walls 7b by going backwards and to shift laterally towards the outside. The implementation of the raised edges 7 c substantially vertical makes it possible, in particular in the curved portions, to prevent the bottles from coming out of the guide 6. For a better understanding of the functionality of the edges 7 c of the guide 6, FIG. 1, in dotted lines, the base of a bottle B 'in its position of maximum lateral rocking in a curve (angle D). In this position, the base of the bottle comes into contact with both the top of the wall guide 7b_ and of the internal face of one of the two edges 7ç_, which allows this bottle B 'to be held inside the guide 6.

In a simpler variant of embodiment of the guide 6, one could however design a guide 6 not having the two vertical edges 7c. Such a guide with a simpler structure could for example be used in the straight portions of a conveyor or in curved portions having a large radius of curvature and for which the lateral rocking angles of the bottles are relatively small.

In the particular variant of the embodiment of FIG. 1, the internal face of the two guide walls 7b forms a plane PP inclined at an angle E being substantially equal to 45 °. This characteristic, although preferred according to the invention, is however not limitative of the invention. In another embodiment, this angle could be more or less important. It is furthermore not essential that the internal face of the two guide walls 7b form a plane, this internal face possibly in other variants having any curved shape, in particular convex or concave.

In accordance with a preferred but non-limiting characteristic of the invention, the lower longitudinal guide 6 is adjustable in position in a vertical plane, which makes it possible to adjust the distance d separating the guide 6 and the guides under the neck 5. The adjustment in height of the guide 6 is obtained in the embodiment of FIG. 1 by means of a plurality of jacks 11 which are mounted on a frame 10 fixed relative to the ground, and which are judiciously distributed over the length of the guide 6. The guide 6 is fixed by any suitable means on the rod 11 'of each cylinder

11. In the example illustrated, the rods 11 'of the cylinders 11 are fixed to the bottom 7a of the guide 6. The displacement of the rod 11' of the cylinders 11 makes it possible to adjust the height position of the guide 6 relative to the guides under collar

5, that is to say, in the embodiment of Figure 1, relative to the point of lift of the bottles via their flange C.

This characteristic advantageously makes it possible to produce a multi-format air conveyor, that is to say a conveyor which can easily be adapted to transport bottles of various shapes and sizes. It is thus possible by reducing the distance d to reliably transport bottles of smaller dimensions than the bottle B illustrated in FIG. 1 and for example bottles such as the bottle B "illustrated in dotted in FIG. 1. Also, it is understood that by adjusting the distance d separating the guide 6 from the upper lift point of the bottles, two adjustments are made simultaneously and simply by means of the guide walls 7b: the minimum conveying angle To bottles; the lateral guide of the bottles is adjusted according to the shape and size of the bottles.

It is up to the person skilled in the art to adjust the distance d separating the lower longitudinal guide 6 from the bottle lift point on a case-by-case basis, so as to obtain a minimum conveying angle A which makes it possible to obtain the best conveyability of the bottles. In practice, after carrying out tests with different formats of bottles, it was found that for most of the bottles existing on the market, the bottles were transported under optimal conditions by adjusting the minimum conveying angle A between 2 ° and 20 °, and preferably between 5 ° and 10 °, the choice of the angle in this range of values having to be made on a case-by-case basis empirically by a person skilled in the art for a given type of bottles. These values of minimum conveying angle A are, however, given purely by way of indication, and are not limitative of the invention, the invention being able to be implemented with minimum conveying angles A outside of the above-mentioned range of values. .

FIG. 3 shows another alternative embodiment of an air conveyor in which the lower longitudinal guide 6 ′ is produced in the form of two identical longitudinal sections 12 mounted parallel to each other, and each comprising a longitudinal flat part 13. These two sections 12 are mounted so that the flat parts 13 are opposite one another and each form a plane PP inclined with respect to the vertical by an angle E. These two flat parts 13 correspond and fulfill the same function as the internal faces 8 of the two guide walls 7b_ of the guide 6 of FIG. 1. Preferably, the two profiles 12 are made of a material with a low coefficient of friction and for example made of plastic type PE (Polyethylene).

In the variant of FIG. 3, unlike that of FIG. 1, the transport under the action of air jets of the bottles along the conveyor is not carried out by means of transport air jets upper generated above the point of lift of the bottles (guide under neck 5) but is carried out exclusively by a side blowing by means of transport air jets J 'which are directed on the bottles below their point of lift. More particularly, in the particular variant illustrated in FIG. 3, the guides under the neck 5 are rigidly fixed on a rail 28 forming a closed cowling except for its underside which is open, this cowling making it possible to protect the neck bottles above their rim. For the formation of the transport air jets J ′, the conveyor comprises two blowing ducts 14, which are arranged on either side of the path of the bottles B. Each duct is designed to be supplied with pressurized air via a automatic supply duct 15. Each blowing duct 14 further comprises a longitudinal face 14a which is oriented towards the bottles and in which are formed slots or blowing openings 16, similar to the slots or blowing openings 4 of the conveyor of the figure 1.

The air conveyor of FIG. 3 also comprises two additional blowing ducts 17 which are designed to generate reverse lower air jets R in the direction of the bottles, that is to say air jets oriented on the bottles au- below their point of lift, but in a direction opposite to the SDT transport direction of the bottles. To this end, each blowing sheath 17 also has at its face 17a oriented towards the bottles a plurality of blowing slots 18. In the particular variant illustrated in FIG. 3, a blowing sheath 14 and a blowing sheath 17 are made by means of the same box separated into two upper and lower compartments by a separating plate 19, the upper compartment forming the blowing sheath 14 for the formation of the transport jets J 'and the lower box forming the blowing sheath 17 for the formation of reverse air jets R. In another variant, the positions of the air ducts 14 and 17 could be reversed. Also, the blowing ducts 14 and 17 could be constituted by two separate boxes, which can be supplied with pressurized air independently or not. In the variant of FIG. 3, the supply of pressurized air to the blowing duct 17 is carried out by means of the duct 14 and a inlet opening 20 provided in the partition wall 19. At this inlet opening 20 is mounted an air distribution slide 21 provided to be actuated between a high position and a low position by a jack 22. In the high position (position of the drawer 21 on the right in FIG. 3), the drawer 21 connects the air intake duct 15 to the opening 20, isolating the interior of the blowing duct 14 from the intake duct 15, and connecting the interior of the blowing duct 17 directly with this intake duct 15, which makes it possible to generate reverse air jets R in the direction of the bottles. Conversely, in the low position, such as in the position of the drawer 21 on the left in FIG. 3, the interior of the blowing duct 17 is isolated from the intake duct 15, which allows the air supply to the blowing duct 14 and thereby the formation of transport air jets J 'towards the bottles. In operation, the drawers 21 on the left and on the right will either be in the high position (generation of reverse air jets R on the bottles to, for example, unlock, or slow down and possibly stop the bottles in a given way in a given section of the conveyor) , or in the low position (generation of transport air jets J 'towards the bottles) to propel the bottles in the normal direction of transport SDT. It is also possible with the conveyor of FIG. 3, to reverse the normal direction of transport of the bottles in the conveyor, the roles of the air jets coming from the blowing ducts 14 and 17 being in this case reversed. The conveyor is thus perfectly reversible from a point of view of the normal direction of transport of the bottles, and this in an easy and rapid manner, without requiring any structural modification of the conveyor.

In the variant of FIG. 3, the blowing ducts 14 and 17 are supplied from the same source of pressurized air. In another variant, these blowing ducts could be supplied independently from different air sources. Also, it is possible in another alternative embodiment, to supply the blowing ducts 14 and the two blowing ducts 17 from the same source of pressurized air, but by distributing the air not by means of drawers 21, but by supplying each blowing duct 14, 17 with secondary connections connected to the common air source, each secondary connection being equipped with a damper, or any other equivalent means, making it possible to control the air supply to the corresponding duct.

One of the advantages of the air conveyor of Figure 3 compared to the conveyor of Figure 1 is related to the fact that the air jets (transport J 'or reverse R) are directed on the bottles in an area located below their point of lift, which limits the risks that the air may be in direct contact with the neck of the bottles and / or may penetrate inside the bottles B and come to contaminate them. Conversely, in the case of the conveyor of FIG. 1, in order to avoid the risks of contamination of the interior of the bottles transported by the transport air jets J, it is imperative to filter with all the required precautions the air which is introduced under pressure inside the blowing duct 1, which requires the use of high performance filters which are expensive. In the case of FIG. 3, knowing that the air jets are not generated above the collar, the risks of contamination are reduced. In addition, in order to further reduce these risks, the air conveyor is equipped with two deflection walls 23 arranged on either side of the path of the bottles, and making it possible to obstruct an ascent of air coming from the blowing ducts. 14 and 17 towards the neck of bottles B.

In the variant of FIG. 3, the guide 6 ′ does not include portions fulfilling the previously described function of the raised edges 7c of the guide 6 of FIG. 1. However, the conveyor of FIG. 3 has two lateral guides 24, which are positioned near the guide 6 'and which allow in particular in the curved portions of the conveyor to limit the angle of lateral movement of the bottles and to prevent the bottles from accidentally coming out of the guide 6'.

It should be emphasized that prior to the invention, it was already known to transport bottles suspended under the action of air jets generated below the point of lift of the bottles and to obtain the aforementioned advantage, it that is to say to limit the risks that the air may be in direct contact with the neck of the bottles and / or may penetrate inside the bottles B and come to contaminate them. However, to date, this lower blowing has been carried out to the detriment of the proper conveying of the bottles, the latter tending under the action of the transport air jets to oscillate towards the front by a greater angle comparatively to a blowing carried out exclusively above the flange such as in the case of the conveyor of FIG. 1. Thanks to the use of a lower longitudinal guide according to the invention, this drawback is now eliminated. Indeed, the lower blowing (air jets J 'in FIG. 3) makes it possible to apply an aeraulic thrust force on the bottles between two support points (upper support on the guides under neck 5 and lower support on the longitudinal guide 6 ') and thereby achieve a perfectly stable conveying of the bottles. The stability of the cylinders during transport is obtained whatever the aeraulic power involved and the point of application of the aeraulic thrust force, that is to say in other words the power and the position of the jets d transport air relative to the body of the bottle.

More particularly, in the embodiment of Figure 3, similarly to the example of Figure 1, the relative position of the lower longitudinal guide 6 'formed by the two sections 12, as well as the relative position of the guides lateral 24, are adjustable in height relative to the guides under neck 5. This height adjustment is obtained by mounting the guide 6 'and the lateral guides 24 on a slide 25 movable along a vertical axis between two columns 26, via cylinders 1 1, whose rod 11 'is rigidly connected by any means suitable for the slide 25. The cylinders 11, the frame 10, the columns 26, the blowing ducts 14 and 17, the bridges 27 and the rail 28 supporting the guides under neck 5 form a fixed assembly with respect to the ground.

Another alternative embodiment is shown in FIG. 4, which is fairly close to the variant of FIG. 3 and which differs essentially therefrom by the fact that the lower longitudinal guide 6 ′ constituted by the two sections 12 and the two lateral guides 24 are fixed in position relative to the ground and the adjustment of the distance separating the two guides under the neck 5 of this guide 6 'and the lateral guides 24 is carried out by modifying the position relative to the ground of the guides under the neck 5. To this end, the rail 28 supporting the guides under the neck 5 is movable along a vertical axis by being mounted on a plurality of slides 25 which are judiciously distributed over the length of the conveyor and which are vertically movable between two columns 26. Each slide 25 can be moved vertically by means of a jack 11 whose rod 1 1 'is rigidly connected by any means suitable for the slide 25. The jacks 11, the frame 10, the columns 26, the air ducts 14 and 17, the bridges 29, the lower guide 6 'and the lateral guides 24 form a rigid and fixed assembly with respect to the ground.

The height adjustment, in the variant of FIG. 3 of the lower longitudinal guide 6 'and of the lateral guides 24, and in the variant of FIG. 4 of the guides under the neck 5, can indifferently according to the invention be controlled automatically. or manual.

Claims

1. Air conveyor for the transport of articles suspended under the action of air jets characterized in that it comprises a lower longitudinal guide (6; 6 ') which extends along the path of the articles, which comprises two opposite longitudinal guide walls (7b_; 13), and which is positioned or is capable of being positioned relative to the point of lift of the articles so that an article suspended on the conveyor comes into contact at the level from its base with the internal face of the two guide walls while being kept inclined relative to the vertical and rearward relative to the direction of transport at a minimum conveying angle (A).

2. Conveyor according to claim 1 characterized in that each guide wall (7b; 13) of the lower longitudinal guide (6; 6 ') has a flat internal face which forms an inclined plane (PP) relative to the vertical, the planes (PP) formed by the two guide walls converging towards each other downwards.

3. Conveyor according to claim 2 characterized in that the inclined planes (PP) formed by the internal faces of the two guide walls of the longitudinal guide are inclined relative to the vertical by the same angle (E).

4. Conveyor according to claim 3 characterized in that the angle (E) is substantially 45 °.

5. Conveyor according to any one of claims 1 to 4 characterized in that it comprises two lateral guides (7c; 24) making it possible to limit the lateral movement of the articles.

6. Conveyor according to claim 5 characterized in that the two lateral guides are formed by two upper edges (7c) of the longitudinal guide (6).

7. Conveyor according to claim 6 characterized in that the internal face (8 ') of each upper edge (7ç_) of the guide (6) forms a plane

(P'P ') substantially vertical.

8. Conveyor according to any one of claims 1 to 7 characterized in that the position of the lower longitudinal guide (6; 6 ') relative to the lifting point of the articles is such that the minimum conveying angle (A) of the items is between 2 ° and 20 °, and preferably between 5 ° and 10 °.

9. Conveyor according to any one of claims 1 to 8 characterized in that it is equipped with means for adjusting the distance (d) separating in a vertical direction the lower longitudinal guide (6; 6 ') and the point of levitation of articles.

10. Conveyor according to claim 9 characterized in that the adjustment means comprise a plurality of jacks (11) distributed along the conveyor.

11. Conveyor according to any one of claims 1 to 10 characterized in that the means for forming transport air jets for propelling the articles along the conveyor are designed so as to generate at least air jets lower (J ') which are directed on the articles below their point of lift.

12. Conveyor according to any one of claims 1 to 10 characterized in that the means for forming the transport air jets for the propulsion of the articles along the conveyor are designed so as to generate exclusively lower air jets (J ') which are directed on the articles below their point of sustenance.

13. Conveyor according to claim 11 or 12 characterized in that it comprises, for the formation of the lower transport air jets, at least two blowing ducts (14) which extend on either side of the path articles, which are designed to be supplied with pressurized air, and which each have a face (14a) oriented towards the articles in which are provided slots or blowing openings (16) for the exhaust of pressurized air inside the sheath in the form of air jets for lower transport (J ').

14. Conveyor according to any one of claims 1 to 12 characterized in that it comprises means for generating reverse air jets (R) oriented in the direction opposite to the direction of transport (SDT) of the articles.

15. Conveyor according to claim 14 characterized in that the reverse air jets (R) are directed on the articles below their point of lift.

16. Conveyor according to claim 15 characterized in that the means for forming the reverse air jets comprise two sheaths of blowing (17) which extend on either side of the path of the articles, which are designed to be supplied with air under pressure, and which each have a face (17a) oriented towards the articles in which slots are provided or blowing openings (18) for the exhaust of pressurized air inside the duct in the form of reverse air jets (R).

17. Conveyor according to claims 13 and 16 characterized in that the blowing sheath (14) for the formation of transport air jets (J ') and the blowing sheath (17) for the formation of air jets inverses (R) are constituted respectively by the two superimposed compartments of a blowing box.

18. Conveyor according to claim 17 characterized in that the air distribution between the two blowing ducts (14,17) of a box is carried out by means of drawer distributors (21) actuated by jack (22).